Technology review
Developments in temperature sensing technology continue to enable disruptive applications
Whatever the material may be, if it demonstrates a correlation between temperature and resistance then it is likely to follow one of two possible patterns; a negative or positive temperature coeffi cient (NTC/PTC).
Thermistors are the most common devices that demonstrate this and, along with resistance temperature detectors (RTD), represent two of the most widely used temperature sensing devices. Both use changes in their resistance to signal a change in temperature. In the case of the NTC, this is normally sudden and non-linear, which is why they are often used to signal a critical change in temperature; one common use for NTCs (whose resistance drops with increasing temperature) is to turn a fan on in an enclosure. Conversely, PTCs, whose resistance increases with temperature, can be used as thermal resettable fuses, however this application needs to be considered carefully because fuses generally fail for a reason! RTDs, on the other hand, typically exhibit a more linear change in their resistance with temperature, and so can be used in more subtle ways.
Semiconductor technology is increasingly used in the design and manufacture of temperature sensors. Temperature causes measurable changes to the transfer function of a transistor’s junction, which means it can be directly used to determine temperature. This is a method
commonly used in integrated circuits but temperature can also be sensed optically, using sensors that are sensitive to the infrared part of the spectrum.
As the way we measure temperature has developed so too have the ways in which we use that information, thanks to advances in processing at the edge. For example, the use of artifi cial intelligence is increasingly being used to identify trends in temperature fl uctuations over a defi ned period. Analyses may show that these correlate with the effects of known conditions, subsequently allowing corrective actions to be taken.
The Braster Breakthrough
Detecting and measuring thermal anomalies in blood cells, known as thermography, is emerging as a potentially useful way of diagnosing breast cancer, particularly in areas of the world where mammograms are not available. It was approved in 1982 by the U.S. Food and Drug Administration (FDA) and is currently offi cially classifi ed by the FDA as an adjunctive tool, meaning it should be used alongside a primary method such as mammography; effectively an x-ray using low doses of radiation. However its use is growing and it is arguably becoming an important form of early diagnosis.
It works by identifying an increase in temperature at, or just below, the skin. This can be the result of increased blood fl ow triggered by the body in order to support the growth and multiplication of cancer cells. Using thermal image sensors positioned close to the skin, these small variations in temperature can be detected in a painless and non-intrusive way.
“As the way we measure temperature has developed so too have the ways in which we use that information, thanks to advances in processing at the edge.”
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A number of companies are pursuing thermography as a way to increase the availability of early diagnosis tools for breast cancer. One of them, Braster S.A. based in Poland, has pioneered the use of liquid crystal contact
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